1. Field of the Invention
The present invention relates in general, to video surveillance and video storage systems and more specifically, to a system and method for automatically controlling the video frame rate of video streams.
2. Discussion of the Related Art
Many applications in the field of video surveillance and video storage require the transfer of video data such that the video frame rate is specifically controlled. These applications should typically involve an input process to generate video frames at the basic rate of the input process, and an associated output process, which requires video frames at a rate specifically required by the output process. Video frame rate adaptation is required in the video surveillance and storage field to solve several basic implementation issues.
Surveillance systems require the ability to view video clips either in real time where the data is available substantially simultaneously with an actual recording or off-line by utilizing previously recorded video data, which is typically stored in a local or remote archive. The best-known and available communication media for remote video viewing is the Internet. Access to a plurality of video files stored across the Internet is readily provided by substantially any standard computing device. To access, to transfer and to view video via from the Internet does not require specific installations of unique hardware or software components. Standard Web browser utilities, such as the Internet Explorer or the Netscape Navigator, which is typically pre-installed in the majority of computing devices, and similarly pre-installed standard widely available communication devices, such as modems or network interface cards, provide ready accessibility to video images over the Internet.
The drawback of utilizing the Internet as a source media and a transfer media for the transfer and the viewing of video files concerns the lack of Quality of Service since there is typically no guarantee for a fixed-rate transmission bandwidth availability. Currently, the transmission rate of the data during Internet sessions fluctuates significantly. Thus, the attempts to achieve a pre-determinedly fixed transmission data rate for viewing pre-determinedly fixed frame rate video is not practical.
Video information archiving requires relatively high storage capacity. In the surveillance field, when video recordings, captured by a plurality of Close Circuit Television (CCTV) video cameras, needs to be archived for substantially extended periods, the required storage capacity might become a considerable cost issue. As a result, in many situations it would be economical to control the size of the required storage space by adjusting the archived video frame rate to the availability of the storage space.
Surveillance systems are characterized by the necessity to provide alarm signals and dynamic recording functions for identified events that typically occur at rare instances. In a surveillance system an event constitutes an electronic trigger generated by some device that senses disturbance in the environment. An event might be generated for example, by the opening of a door or a window in the environment under surveillance, which is captured by a movement-sensing device or by a video motion detector. Most of the time, the systems monitor a substantially static environment, which does not provide significant event-specific information. Thus, for extended periods the surveillance systems operate typically in a “wait-state” during which continuous attempts are made in order to identify critical events. It is imperative that critical events would be recorded and that simultaneously generate an associated alarm signal. When a critical event occurs, the recording of the video needs to be performed with the highest possible quality. In the “wait-state”, during the substantially static or “quite” periods, a lower recording rate, requiring less storage space, could be activated in order to provide a better trade-off.
One obvious solution might be to switch to a higher recording rate when the event happens. The drawback of this solution is that an inevitable minor delay between the event and the start of the high recording rate could effect the missing of some of the important information that is in the video images representing the event occurrence.
Surveillance systems often require the capability of monitoring the same video source, such as a video camera, where the recording is to be transmitted to several viewers, where each viewer is having its own bandwidth viewing capability in accordance with the respective communication devices, communication lines, location, viewing apparatus and the like. When using conventional analog CCTV cameras, the multi-monitoring capability is usually provided via amplifiers, splitters, and coaxial cable routing the signal to the various users. When using video cameras having digital (Web enabled) output (typical example is model # 2420 manufactured by AXIS Communications of Lund Sweden), the distribution of the video to several viewers is more problematic. One solution might be the use of multi-cast IP massages that are routed to the users that are in the addressee list of the multi-cast massage. The drawback of this solution is that all the users will get the same information rate that will have to be reduced to the lowest common denominator.